How to change the value in data in uniapp method

UniApp is a cross-platform development framework that can be developed and deployed on multiple platforms. In UniApp development, we often need to change the value in data in the method to implement business logic. However, if we don't understand how data is used in UniApp, we may encounter some problems.

In UniApp, we can declare data through the data attribute of the component, and use the setData method in the component method to change the value in data. The setData method is asynchronous, so we need to pay attention to the writing method.

The following is an example:

<template>
  <view>{{message}}</view>
</template>

<script>
export default {
  data() {
    return {
      message: 'Hello World!'
    }
  },
  methods: {
    changeMessage() {
      this.setData({
        message: 'Hello UniApp!'
      }, () => {
        console.log('data已经更新'); // data已经更新
      })
    }
  }
}
</script>

In the above example, we declared a data attribute named message and used it in the component's template. In the component method, we change the value of the message by calling the setData method. It should be noted that we use a callback function in the second parameter of the setData method to perform other operations after the data is updated.

In addition, it should be noted that although we use the this.setData method to update the page data, this is actually what the Vue framework does at the bottom. The Vue framework will automatically update the page when the data is updated. Therefore, the way to update page data in UniApp is different from that in pure JavaScript.

In addition to using the setData method in the method to change the value in data, we can also calculate new values ​​based on the value of data through calculated properties. The following is an example:

<template>
  <view>{{fullName}}</view>
</template>

<script>
export default {
  data() {
    return {
      firstName: '张',
      lastName: '三'
    }
  },
  computed: {
    fullName() {
      return this.firstName + this.lastName
    }
  }
}
</script>

In the above example, we declare two data properties named firstName and lastName, and calculate a new one based on the values ​​of these two properties in the calculated property fullName value. The computed property fullName is ultimately used in the template of the rendered component.

In addition to the above methods, we can also use the watch method to monitor data changes and perform some operations when the changes occur.

In short, in UniApp, we can change the value in data through methods, calculated properties and watch methods to implement corresponding business logic. It is important to understand the asynchronous nature of the setData method and note that the page data is updated differently than in pure JavaScript.

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